Skin problems are pervasive in society. People suffer from conditions ranging from the cosmetic, such as benign discoloration, to fatal ailments, such as malignant melanomas. Treatments: range from cosmetic xe2x80x9ccover-upxe2x80x9d makeup to surgical excision.
In particular, the removal (or xe2x80x9cskin peelxe2x80x9d) of an outer layer of skin is used to treat conditions such as acne, age spots (superficial regions of excess melanin), shallow lesions (e.g. actinic keratoses), and aged skin. FIG. 1 depicts a cross section of normal human skin. The depth of the outer layer, or epidermis, varies, with ranges typically from 50-150 xcexcm in thickness. The epidermis is separated from the underlying corium (dermis) by a germinative layer of columnar basal cells. The epidermal/dermal interface is characterized by undulations. The basal cells produce a continuing supply of keratinocytes, which are the microscopic components of the epidermis. Specialized cells called melanocytes, also reside in the basal cell layer and produce the pigment melanin. Although some of the melanin migrates toward the surface of the skin with the keratinocytes, the greatest concentration of melanin remains in the basal cell layer. The uppermost layer of the dermis, which is adjacent to the basal cell layer, is known as the papillary dermis, and the papillae range in width from 25-100 xcexcm, separated by rete ridges (xe2x80x9cvalleysxe2x80x9d) of comparable width.
Removal of the epidermis eliminates superficial sun damage, including keratoses, lentigenes, and fine wrinkling. Removal of the most superficial portions of the dermis, i.e. the uppermost papillary dermis, eliminates solar elastosis and ameliorates wrinkling, with little or no scarring.
One treatment that is currently very popular uses a short pulse carbon dioxide (CO2) laser to coagulate a layer of skin to a depth of xcx9c50-100 xcexcm /pulse. This treatment is sometimes referred to as a xe2x80x9claser peel.xe2x80x9d CO2 laser radiation (in the 9-11 xcexcm region of the infrared) is strongly absorbed by water (contained in all tissue). When the energy/unit volume absorbed by the tissue is sufficient to vaporize the water, a microscopically thin layer of tissue at the surface of the irradiated region is rendered necrotic; (see e.g., R. M. Adrian, xe2x80x9cConcepts in Ultrapulse Laser Resurfacing,xe2x80x9d URLxe2x80x94http://www.lasersurgery.com/physicians.html (1996)). The skin is coagulated on the surface of the region irradiated by the infrared beam from the CO2 laser. After irradiation, the dehydrated, necrotic surface layer is mechanically removed, and additional irradiation takes place, this process being repeated until the desired depth of tissue is removed. In medical terms, tissue is removed with less collateral damage than with other modalities, e.g., liquid nitrogen, cautery, chemical peels; (see e.g., E. V. Ross et al, xe2x80x9cLong-term results after CO2 laser skin resurfacing: a comparison of scanned and pulsed systems,xe2x80x9d J Amer Acad Dermatology 37: 709-718 (1997)).
The radiation features that result in reduced collateral damage are: a wavelength that is strongly (optically) absorbed; and a pulse duration that is short compared to the time for deposited energy to diffuse into the surrounding tissue; (see e.g., R. J. Lane, J. J. Wynne, and R. G. Geronemus, xe2x80x9cUltraviolet Laser Ablation of Skin: Healing Studies and a Thermal Model,xe2x80x9d Lasers in Surgery and Medicine 6: 504-513 (1987)). The short pulse CO2 laser, with an absorption coefficient in tissue of xcx9c{fraction (1/50)}xcexcmxe2x88x921 and a pulse duration of xcx9c10-100 ns, leads to a reduction of collateral damage as compared to a continuous wave (cw) CO2 laser or lasers at other visible and near infrared wavelengths. But clinical results on patients treated for the elimination of wrinkles with the short pulse CO2 laser show an abundance of undesirable aftereffects, including erythema (red, inflamed skin) and crusting, with the possible formation of scar tissue and dyspigmentation. (see e.g., Andrew Bowser, xe2x80x9cAddressing Complications from Laser Resurfacing-Deep scarring and insufficient follow-up are among causes cited,xe2x80x9d Dermatology Times 18, No. 9: 50-51 (Sept. 1997)). One problem with the pulsed CO2 laser is that the radiation absorption depth is not shallow enough. Another is the deposited laser energy is not sufficiently removed from the surface to completely prevent collateral damage. As a result, this modality for xe2x80x9csuperficial skin peelxe2x80x9d can be relatively painful, often requiring general anesthesia and a prolonged recovery period.
A newer treatment that is gaining in popularity uses a pulsed erbium YAG (Er:YAG) laser, emitting radiation at 2.94 xcexcm in the infrared, where water absorption is even stronger than at CO2 wavelengths. Er:YAG light is approximately 10 times more strongly absorbed in skin than CO2 laser light. When compared to the effect of CO2 laser irradiation, a shallower layer of skin absorbs the radiation and is vaporized and ablated from the surface, leaving a thinner thermally damaged and coagulated layer adjacent to the removed tissue. Damage has not been observed to exceed a depth of xcx9c50 xcexcm of collagen denaturation. (See e.g., R. Kaufinann and R. Hibst, xe2x80x9cPulsed Erbium:YAG Laser Ablation in Cutaneous Surgery,xe2x80x9d Lasers in Surgery and Medicine 19: 324-330(1996)).
Treatment with the Er:YAG laser rejuvenates skin, with less pain, less inflammation, and more rapid healing than treatment with the CO2 laser. The depth of penetration with the Er:YAG laser, being shallower, does not thermally stimulate new collagen growth as much as the CO2 laser, so fine wrinkles are not eradicated as effectively. Dermatologists and cosmetic surgeons are,finding the Er:YAG laser preferable for younger patients who have superficial skin damage but less wrinkling, while the CO2 laser is thought to be preferable for older patients who want to have fine wrinkles removed around the lips and the eyes (see e.g., Betsy Bates, xe2x80x9cDermatologists Give Er:YAG Laser Mixed Reviews,xe2x80x9d Skin and Allergy News 28, No. 11: 42 (Nov. 1997)). Although the depth of penetration is shallower and the skin is actually ablated rather than just rendered necrotic, the ablation depth and the depth of coagulated skin limits the precision with which the Er:YAG can remove epidermal tissue without damaging the underlying papillary dermis. And while pain is lessened, many patients still require some sort of anesthesia during treatment and the application of a topical antibiotic/antimicrobial agent following treatment to prevent infection during healing.
It is also generally known in the art to use ultraviolet wavelength lasers for medical and dental applications. See e.g., U.S. Pat. No. 4,784,135, issued Nov. 15, 1988, entitled xe2x80x9cFar Ultraviolet Surgical and Dental Procedures,xe2x80x9d by Blum, Srinivasan, and Wynne. See also U.S. Pat. No. 5,435,724, entitled xe2x80x9cDental Procedures and Apparatus Using Pulsed Ultraviolet radiation,xe2x80x9d issued Jul. 25, 1995 to Goodman, Wynne, Kaufman and Jacobs.
The need remains for an apparatus and method which provides for skin resurfacing in a painless environment with exquisite control and markedly decreased morbidity by eliminating erythema and scarring. There is also a need for an apparatus and method of using ultraviolet (uv) light, delivered in a finely-controlled, countable number of short pulses with sufficient fluence to ablate skin, to remove thin layers of skin at the site of irradiation, with exquisite lateral precision and depth control, resulting in minimal damage to the skin surrounding and underlying the ablated area. The present invention addresses these needs.
There is also a need for an apparatus and process which enables a controlled removal of the epidermis down to the papillary dermis, adapting to the undulations of the papillary dermis. The present invention addresses such a need.
In accordance with the aforementioned needs, the present invention is directed to a system (called a Dermablator) that can be used to carry out an improved xe2x80x9claser peelxe2x80x9d of the skin. The present invention is also directed to a process, Dermablation, that leads to clean, precise removal of surface skin while minimizing collateral damage to the skin underlying the treated region.
An example of a surgical system for removing skin having features of the present invention includes: a pulsed light source capable of delivering a fluence F exceeding an ablation threshold fluence Fth; and a control mechanism, coupled to the light source, for directing light from the light source to locations on the skin and determining if a skin location has been ablated to a desired depth.
The light source is preferably a laser, for example: an argon fluoride (ArF) laser having a wavelength of approximately 193 nm; a krypton fluoride (KrF) laser having a wavelength of approximately 248 nm; a xenon chloride (XeCl) laser having a wavelength of approximately 308 nm; a xenon fluoride (XeF) laser having a wavelength of approximately 351 nm; or an Er:YAG laser.
The present invention has other features which limit the depth of ablation by utilizing feedback from the physiology of the skin, namely the infusion of blood into the area of excision when skin has been ablated to a sufficient depth to produce bleeding. The infusion of blood can act as a xe2x80x9cstopxe2x80x9d to prevent further ablation, thereby effectively terminating the dermablation. The blood can then be removed by washing it away with physiological saline solution, clearing the area for further treatment.
One version of the present invention utilizes a laser having a relatively low blood absorption characteristic, such as an ArF laser, to ablate the skin to a sufficient depth to produce bleeding. A second laser, such as a uv light source with a different wavelength and a relatively high blood absorption characteristic, is then utilized to penetrate the blood, heating it sufficiently to coagulate the blood, stemming subsequent bleeding, yet leaving the tissue with an intact ability to heal without the formation of scar tissue.
An example of such a system, wherein the laser is an ArF laser, further comprises: a coagulating light source having a different wavelength than the ArF laser and a relatively high blood absorption characteristic; means for detecting the appearance of blood at a given skin location;
and means for switching to the coagulating light source, in response to the detection of blood at a given skin location.
Examples of the coagulating light source, include a krypton fluoride (KrF) laser having a wavelength of approximately 248 nm; a xenon chloride (XeCl) laser having a wavelength of approximately 308 nm; and a xenon fluoride (XeF) laser having a wavelength of approximately 351 nm.
The present invention has still other features which provide precise lateral and depth control, permitting the epidermis to be removed down to the papillary dermis, following the undulations of the papillary dermis, so that the papillae are not penetrated even though the epidermis is removed in the adjacent rete ridges. This lateral and depth control may be accomplished by using careful observation, assisted by spectroscopic detection, to identify when the epidermis has been removed, exposing the underlying dermis, with spatial resolution appropriate for the spacing of the undulations of the papillary dermis.
The lateral and depth control of the present invention is one advantage over prior art laser peels operating at wavelengths which lead to thermal damage in the tissue underlying the ablated region that renders this underlying tissue denatured and coagulated. For example, the use of current CO2 lasers make it difficult if not impossible to determine how deep the ablation has penetrated based on real-time observation and/or feedback control.
Accordingly, the present invention has yet other features which provide a feedback control mechanism which utilizes the optical characteristics such as the color, appearance and remittance of the defmable skin layers. Using ultraviolet light ablation, the tissue underlying the ablated region will retain its undamaged morphology and color, permitting real-time determination of whether the ablation has proceeded to the correct depth, e.g., to or just beyond the epidermal-dermal interface.
Another example of the present invention includes a means for controllably abalating the skin by detecting a color change near or at the epidermal/dermal boundary. The control mechanism could be a feedback control mechanism, comprising: a second light source illuminating the skin; and at least one photodetector having an input and an output; the input receiving scattered/reflected/fluoresced light from the second light source, and the output providing a feedback signal to the system causing the light source to be inhibited at a given location, in response to the second light source at the input. Examples of the second light source include a visible light source; an infrared light source; and an ambient light source. Another example of the second light source is one which is both relatively highly absorbed by epidermal melanin and relatively highly remitted by a dermal layer.
Furthermore, the present invention has features that serve to automate the removal of skin, a wherein the ablating laser beam can be scanned accurately and repeatably over a designated area of skin under the control of a computer system which utilizes real-time observation and/or feedback to control the depth of ablation at each location. The areas to be scanned may be designated by an adjunct visible alignment laser, employing an input device to scan the alignment beam over the area of skin to be treated and recording the beam positions for subsequent automatic scan of the ablating laser beam over the same scan domain. Alternatively, the area of treatment may be specified by recording its image with a camera and designating on the digital image the locations to be treated.
An example of an automated system having features of the present invention includes an alignment and recording mechanism, comprising: a visible laser emitting a beam illuminating the skin at a location coincident with the ablating light; means for scanning the beam across the locations on the skin; and means for recording scanned beam positions, coupled to the means for scanning, for subsequent automatic scan of an ablating light source across the locations on the skin.
An example of the computer and control mechanism includes: one or more rotatable mirrors, the mirrors positioned in the light source path for controllably scanning the light source; one or more motors, coupled to the mirrors, for angularly rotating and feeding back angular positions of the one or more mirrors; and a computer, coupled to the light source and the motors for controlling the motors and selectively shuttering the light source at a given location on the skin.
In yet another example, the computer includes a feedback control system, coupled to the light source for selectively shuttering the light source at a given location on the skin. The shuttering mechanism could be an active mask array, coupled to the feedback control system, for selectively shuttering the light source at a given location that has been ablated to the desired depth.
Still another example of the present invention is a robot/laser system, further including a camera for visualizing an image of the locations on the skin; a computer, coupled to the camera, the computer having an output for displaying and an input for designating the locations of the skin to which the laser is directed.
Preferably, the robot/laser system further includes: one or more rotatable mirrors, the mirrors positioned in the light source path for controllably scanning the light source; one or more motors, coupled to the mirrors, for angularly rotating and feeding back angular positions of the one or more mirrors; a second light source illuminating the skin being ablated, wherein light from the second light source is scattered/reflected/fluoresced from the ablated location; a photodetector having an input and an output; the input for receiving the light from the second light source; and the output coupled to the system and providing a feedback signal to the system for inhibiting the pulsed light source at a given location.
Preferably the robot/laser system includes a registration mechanism for relating coordinates of a point in one patient coordinate frame of reference to a corresponding position in the robot/laser frame of reference. An example of the registration mechanism includes means for attaching fiducials to the skin; a movable tracking laser, coupled to the computer, for recording 3D coordinates of the fiducials; and triangulation means, for establishing 3D locations of the fiducials in the tracking laser frame of reference. Another example of the registration mechanism comprises: means for relating points corresponding to an area of skin in the patient frame of reference subsequent to a change in position, to the same area of skin in a patient frame of reference prior to said change in position. Yet another example of the registration mechanism comprises means for accurately directing the light source by relating points on an area of skin defined in a digital image, to an area of skin on the patient.
An alternative registration mechanism comprises: means for attaching fiducials to the skin; a pair of cameras, coupled to the computer and mounted at fixed positions relative to the robot/laser system for recording coordinates of the fiducials; calibration means for relating the fixed positions of the cameras to the robot/laser system from a predetermined calibration transformation; and a camera model for mapping the relationship between each location in 2D camera images and a set of 3D points in an imaged space that map to it.
Another example a robot/laser system of the present invention includes: a camera for visualizing an image of the locations on the skin; a computer, coupled to the camera, the computer having an output for displaying and an input for designating the locations of the skin to which the laser is directed; a flexible optical fiber bundle having an output end and an input end, the output end being attached to a mask for affixing to the patient and the input end adapted for receiving the light source in a predetermined manner; and a removable mirror located adjacent to the input end for viewing the skin through the fiber bundle using the camera.
In addition to serving to remove cosmetic defects, i.e. seborrheic keratoses and lentigenes, the Derrnablator/Dermablation can provide a modality to treat other pathologies of the epidermis, including Bowen""s disease, exophytic warts, flat warts, lichen-planus-like keratosis (LPLK), and actinic keratoses. Thus, this invention provides an apparatus and process for treating a wide range of common skin conditions.
Furthermore, there are many other applications of this invention: (i) The precise superficial capability of Dermablation allows tissue to be xe2x80x9cmarked,xe2x80x9d i.e., scored with an identifying mark, either on the patient or on biopsy samples; (ii) Localized fungal infection of the toenail may be treated by ablating the infected region to the desired depth without damaging underlying tissue; (iii) Bum eschar (the result of a serious burn) may be removed by ablating it with the Dermablator, following the variable thickness of the eschar and stopping at each location as soon as healthy, viable tissue is uncovered; (iv) Malignant melanoma may be removed by Dermablation with elimination of surgically-induced metastasis, i.e., no viable cancer cells will be released into the patient""s system; (v) Patients with bacterial or viral infection (e.g., AIDS) may be treated with no danger that the tissue ablated from the surface will contain viable viral particles or other microbes, since Dermablation decomposes the ablated material into small inert molecular or atomic fragments; (vi) Patients with the rare condition of Epidermolysis Bullosa, whose delicate skin is incapable of repairing itself following even minor surface cuts and wounds, can have epidermal lesions removed by Dermablation without compromising their fragile dermis; and (vii) Eyelid lesions at the tarsal margin, such as hydrocystoma and Chalazion (sty), may be treated with great precision, resulting in minimal damage to the eyelashes and minimizing the likelihood of notches or other depressions in the tarsal margin that can interfere with tear flow and mucous distribution on the inner surface of the eyelid.
An additional application is to use Dermablation to remove a basal cell carcinoma. Here, the lesion can be selectively marked with an exogenous agent that provides contrast between the lesion and surrounding healthy tissue. Basal cell carcinomas are differentiated from surrounding tissue in biopsy specimens by standard histological treatment, i.e., staining the tissue with chemicals. Such histology is used to make the diagnosis of basal cell carcinoma in the biopsy. Staining agents can be applied directly on the patient, providing a visible differentiation of the basal cell carcinoma, such differentiation being used to guide the Dermablator to remove the lesion with minimal collateral damage.